Flowability responses of cement paste containing steel fiber to external magnetic field

This study explores the magneto-rheological behavior of cement paste using steel fibers as responsive elements. A custom-designed mini-slump device equipped with a camera was employed to capture the real-time flow of cement paste under magnetic fields, considering different water-to-cement (w/c) ratios (0.35, 0.4, and 0.45) and steel fiber concentrations (0%, 1%, 2%, and 3%). The findings demonstrate that the fluidity of cement pastes with steel fibers decreases by 0.7%–8.2% after exposure to a short-term vertical magnetic field, compared to those without magnetic field. After experiencing a horizontal magnetic field, the flow velocity decreases and the flow diameter is smaller in the direction parallel to the field compared to the perpendicular direction. This behavior is more noticeable with increased steel fiber content and w/c ratios, likely due to the flow-restricting effect of residual fiber aggregations formed under the magnetic field. To confirm the residual aggregation behavior of steel fibers in cement paste, the magnetically induced movement of steel fibers in transparent resin solutions was visualized, and their distribution in post-flow cement pastes was examined. It was revealed that steel fibers move under a magnetic field and retain their positions once the field is removed, leading to an uneven distribution. After exposure to a short vertical magnetic field, steel fibers are gathered in the central area, while they concentrate towards the sides following experienced a short-term horizontal magnetic field. These findings provide fundamental experimental support for actively controlling the rheological properties of steel fiber-reinforced cement-based materials.